Rsntp

= rsntp

+rsntp+ is an experimental high-performance NTP server written in Rust. It does not implement a full NTP client and relies on another NTP client and server to be running on the system instead. It periodically updates its state to mirror the real NTP client/server and uses multiple threads to serve the current system time.

By default, +rsntp+ uses one thread for IPv4 and another for IPv6. In order to get the best performance, it's necessary to increase the number of threads using the +--ipv4-threads+ and +--ipv6-threads+ options to correspond to the number of CPU cores available on the system.

The real NTP client/server needs to be configured to listen on 127.0.0.1 on port 11123 (or another port if specified with the +--server-addr+ option). For instance, the following configuration should work with +chronyd+:

allow 127.0.0.1 port 11123 bindaddress 127.0.0.1

The following graphs compare the +rsntp+ performance with +chronyd+ (version 4.1), as measured by https://github.com/mlichvar/ntpperf[+ntpperf+]. The tests ran on a Linux machine with an Intel E3-1220 v6 CPU (4 cores) and a 1Gb/s Intel I350 network card. The maximum rate of NTP requests and responses at the 1Gb/s speed is about 1100k per second.

image::ntpperf.png[]

The graphs show that with +rsntp+ the server starts dropping packets at a higher rate than +chronyd+ and its performance is more stable as the rate of requests is increasing. +chronyd+ does not use multiple threads as a server. It needs to be started in multiple instances sharing the server port in order to utilize multiple CPU cores. It starts dropping packets at a lower rate and the response rate is jumping up and down as the request rate is changing. With both implementations 4 threads/instances are needed on this system to fully saturate the 1Gb/s link without any packets dropped, but +rsntp+ with 3 threads is very close to it.